The temperature of water in the heating tank can be measured with a standard thermometer. Discharge a little water from the relief valve into a container and test its temperature. If it is too high for the rating of the temperature and pressure relief valve, check the thermostat settings on the water heater. Turn the heat settings down and test the water again later after the new temperature settings have had time to work. If the reduction on the thermostat settings does not lower the temperature of the water in the tank, replacement of the tank is usually the best course of action.
if you suspect the water heater is under too much pressure, you can test the pressure with a standard pressure gauge. the easiest way to do this is to adapt to gauge to a hose thread adapter and attach it to the drain at the bottom of the water heater. As long as the drain is not clogged, you can get an accurate pressure reading. You could also adapt the gauge to screw into the relief valve and test the pressure by opening the relief valve.
No Hot Water
when no hot water is being produced by an electric water heater, there are only a few things that need to be checked. The first thing to do is to check the electrical panel to see that the fuse or circuit breaker for the water heater is not blown or tripped. For water heaters that have their own disconnect boxes, check the disconnect lever to see that it is turned on.
Assuming the water heater is receiving adequate electrical power, check the thermostat to see that they are set at a reasonable heat setting. It is highly unlikely that anyone would turn them way down, but it is possible.
The most likely cause of this problem is a bad heating element, but a bad thermostat could also be at fault. Check the continuity and voltage of these devices with the meter to determine if they should be replaced.”
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